Analyzing Seismic Performance of Optimized Base Isolation Systems with Soil–Structure Interaction: An Analytical and Numerical Approach

Abstract

Soil–structure interaction (SSI) is a well-established phenomenon with significant implications for the dynamic response of structures subjected to earthquake loads. This study aimed to find the optimum stiffness of a lead rubber bearing (LRB) isolator within a multi-degree-of-freedom (MDOF) structure using a genetic algorithm (GA) while accounting for SSI effects through analytical formulation and numerical simulation. The simplified linear cone model was utilized to model the SSI effect, with two degrees of freedom of the soil: sway and rocking. Analytically, the main contribution is the presentation of an equivalent frequency formula for both the structure and the isolation layer, allowing the presentation of these later with respect to dimensionless parameters. Numerically, the displacement of the base level was targeted as the response to be reduced through the GA optimization, which is a further contribution of this work. To achieve this, 28 earthquake records with two components each were used during the optimization procedure. These records were regarded as near-field excitations, and 14 of them had pulse-like characteristics while the other 14 did not. The obtained results showed a local optimum of isolator stiffness for each earthquake and soil type. Owing to the stochastic nature of earthquakes, a weighted averaging method was used to obtain the global optimum isolator stiffness for each soil type, which is a novelty in this work. Further investigation of the local and general optima in the time and frequency domains showed a significant reduction in response in terms of base-level displacement, root-mean square (RMS) of top-floor acceleration, and strain energy of the entire structure. These findings may represent added values for designers working on base isolation (BI) devices in various soil conditions.